1. Field of the Invention
The present invention relates to the field of signal processing. More specifically, the present invention relates to the processing of measured signals which contain a primary signal portion and a secondary signal portion for the removal or derivation of either signal portion. The present invention is especially useful for physiological monitoring systems, including blood oxygen saturation measurement systems and oximeters.
2. Description of the Related Art
Blood oxygen saturation measurement systems, oximeters, and physiological monitors of the prior art generally utilize two different wavelengths of light to determine a patient's blood oxygen saturation level. In general, such systems provide two wavelengths of light to a target location on a patient's body. The systems then measure at least one signal indicative of the transmission or reflection of the two light wavelengths with respect to the tissue at the target location.
One such physiological monitor is taught by Diab et al. in U.S. Pat. No. 5,632,272, incorporated by reference in its entirety herein. One embodiment of Diab's physiological monitor provides light having a red wavelength and light having an infrared wavelength to one side of a patient's finger. A detector on the opposite side of the patient's finger measures the red and infrared wavelength light transmitted through the patient's finger and generates a measurement signal. A processor analyzes the measurement signal to determine red and infrared component signals. Possible saturation values are input to a saturation equation module which provides reference coefficients. The red or infrared component signal is processed with the reference coefficients to yield reference signal vectors.
The reference signal vectors and the red or infrared component signal are processed by a correlation canceller to generate output vectors. The output vectors are input into a master power curve module, which provides a blood oxygen saturation value for each possible saturation value input to the saturation equation module. The patient's blood oxygen saturation is determined based upon the power curve module output.